In this design, both the submersible pump and its driving motors are installed totally submerged in the deep waters. The motor has weather proof. The pump portion is identical to vertical turbine pump.
The history of submersible dates back to 1908, the year in which it was invented. Thus pump initially found most veritable due to naval application for salvaging purpose and then gained popularity for deep well application.
Since 1990, they found tremendous application in the field of irrigation engineering as well as mine dewatering with improved materials, and construction submersible pumps continues to find various new application as circulating water pumps, fuel handling pumps, pumps in fishing trawlers and in oceanography.
Construction and Working details of Submersible Pumps
In submersible pump set, both pump and motor are installed deep inside the tube well, so that the suction head is minimized which make it possible to lift water from depth as low as 450 m. Thus pump may be single stage or multi-stage type and it coupled with wet type squirrel-cage induction motor, both of which operate totally submerged below the surface of water.
Submersible pumps with radial impeller are made for low discharge with total high heads, where as pumps with mixed flow type impeller, are made for medium discharge range with medium heads.
The pump bearings are water lubricated and protected against the ingress of sand by suitable structural elements. The casing of radial impeller are clamped together by flat steel tie bars. The individual casing of mixed flow impellers are connected perpendicular one another by stud bolts. The non-return valve located at the top of the pump in discharge outlet connection is fully stream lined for smooth flow. The pump suction casing between the pump and motor is guarded by perforated strainer to prevent entry of any suspended materials in the water.
Wearing ring is fitted on each stage bowl and inlet body, with the result, that only wearing ring is to be replaced in the case of damage or wear and tear of the stage bowl and inlet body. Similarly renewable shaft protects sleeve of the non-ferrous material is provided on each stage which protects shaft in case of damage of the bowl.
Submersible motors are wet type squirrel cage induction motors completely filled with pure clean water. They consist of waterproof insulated winding. All the motors are sealed effectively against water contamination, both at the top and bottom.
The axial thrust generated by the pump is observed by a thrust bearing arranged at the bottom of the motor. A breather diaphragm is provided beneath the thrust bearing which compensates the pressure, which arises as a result of thermal expansion of water filled in the motor.
The work of submersible pump is similar to the working of vertical turbine pump similarly i.e. by the impeller rotates inside pump, vacuum is created, to fill up the vacuum water is enter into the impeller, the pump has radial flow impeller, therefore it discharges the water in the radial direction, due to bowl assembly it changes the radial direction of water to axial direction of water and facilitate the direction of water into another impeller which are arranged in series manner in case of multi-stage of submersible pump.
Advantages of Submersible Pumps
- Installation requires no foundation, therefore it is very easy to install
- As the pump rests below water level, flow inside the pump is automatically and no suction difficulties arise
- As the bearings are water lubricated, periodical oiling or greasing is not needed. Therefore it need almost no maintenance
- Both the pump and motor are placed deep down in the well, there is no disturbance from pumping noise
- The slim rotor designs effects quick starting since the internal mass (inertia) of the rotor is very low
- The overall efficiency is so higher than that of the vertical turbine pumping
- In general, vertical turbine pumps are preferred up to 45 m depths. For depth more than 45 m, the only choice is submersible pumps.
Submersible pumps are sturdy in case of occasional applications like pumping out floodwaters from a certain locality, temporary pumping installations because they do not require any foundation and can be suspended from the top.